The post Jellyfish Day Celebrates 500 Million Years of Ocean Wonder appeared first on A-Z Animals.
If one were to mention December 25th, most people, regardless of their religious affiliation, would probably think of Christmas. How about October 31st? That’s right: Halloween. February 14th? You got it: Valentine’s Day. November 3rd?… Anybody?… No? Well, it’s Jellyfish Day, of course!
This unofficial holiday celebrates one of the ocean’s most misunderstood creatures. In the minds of most, the jellyfish is that neat-to-look-at but God-help-you-if-it-stings-you translucent creature you may come across on the beach, but it is so much more. Jellyfish have graced this planet for more than 500 million years! They’ve outlasted dinosaurs, ice ages, and seen the rise of human beings. On this Jellyfish Day, let’s all take a little time to honor these extraordinary, essential, beautiful creatures.
Ancient Wonders
Jellyfish have been on Earth for more than 500 million years.
©pluuuuuuuuus/Shutterstock.com
Fossil evidence suggests that jellyfish are one of the first complex multicellular animals ever on Earth, predating fish, insects, and even trees. They’ve weathered several mass extinctions that wiped out countless other species. What makes their endurance even more remarkable is the abject simplicity of their design: they have no brain, no bones, and no blood. They are essentially a bell-shaped blob of pulsating tissue, powered by a network of nerves.
As far as researchers can tell, their basic body plan has remained remarkably consistent over hundreds of millions of years. The aforementioned bell-shaped blob is called the medusa. The medusa propels the jellyfish by contracting, then relaxing, which pushes water behind it in soft pulses. Their long tentacles are lined with stinging cells, called nematocysts, which are used to capture plankton, larvae, and small fish. Each nematocyst contains a coiled, venom-tipped thread that delivers a toxin strong enough to subdue prey, ward off predators, or seriously ruin the afternoon of an unsuspecting beach-goer!
The simple jellyfish is a marvel of efficiency, able to thrive without organs that are essential to most other animals. Certain species have complicated eye-like structures that can sense colors and shapes, but most jellyfish detect light and obstacles and sense direction simply through their network of nerves. There are even some species, the box jellyfish, for example, that have shown signs that suggest their ability to learn, despite the fact that they don’t have a brain!
It would seem, since jellyfish appear to just drift along with the tides, that jellyfish are passive creatures, but it’s actually the opposite: research increasingly shows jellyfish to be active navigators, orienting themselves and adjusting to light and the patterns of the currents. There are even some species that vertically migrate every day, rising to the surface at night to feed and sinking down during the day to avoid predators.
If you were to pick up a jellyfish (not recommended!), it would seem to disappear in your hands. This is because the jellyfish’s body, what little there is of one, is about 95 percent water, with the remaining five percent being made up of collagen-like proteins and salts. This ratio of water to solids makes them naturally buoyant, allowing them to easily drift along the plankton-rich upper layers of the sea. This efficiency is a big part of their success, requiring minimal energy for them to move or eat. Furthermore, when food is scarce, they’re able to shrink in size, which reduces their metabolic needs until such time as conditions improve and they can grow again. This adaptability contributes to the occurrence of “jellyfish blooms,” phenomena in which jellyfish populations sometimes surge in warmer or more disturbed oceans.
And They Glow!
The jellyfish’s ability to glow has aided humans in cancer research.
©YouTube/EVNautilus
Another fascinating characteristic of the jellyfish—one so beautiful and magical it hardly seems real—is bioluminescence, the ability to produce light through chemical reactions. Essentially, this means jellyfish can glow in the dark. And while this is absolutely incredible to look at, it does serve an evolutionary function as well, startling away predators while at the same time attracting prey. Not only that, but this unique ability has helped humans as well. The Aequorea victoria, a transparent jellyfish native to the Pacific Northwest, contains a molecule called green fluorescent protein (GFP), which has revolutionized cell biology since its discovery in the 1960s, being used to tag and visualize genes and proteins in everything from neuroscience to cancer research.
A Crucial Part of the Ecosystem
Not only are jellyfish amazing creatures in and of themselves, but they are major contributors to the overall marine ecosystem. Both predators and prey are a crucial link between microscopic plankton and larger ocean animals. Juvenile fish will often hide amid a jellyfish’s tentacles for protection. Sea turtles rely on jellyfish as a primary food source (an adult leatherback sea turtle can consume large quantities of jellyfish daily, sometimes totaling several dozen, depending on the size of the prey).
When they die, jellyfish sink and form a “jelly-fall,” which delivers organic matter to the deep sea and feeds scavengers that live at depths where sunlight doesn’t reach, contributing to the ocean’s carbon cycles by transferring carbon from the atmosphere to the deeper parts of the ocean. And while massive blooms can be disruptive to fisheries or clog power-plant intakes, they’re also excellent indicators of changing ocean conditions. Since jellyfish flourish in stressed ecosystems, such as warming waters, pollution, or overfishing, a surge in their population acts as a warning sign of how human activity is affecting a marine environment.
Are Jellyfish Going to Take Over the Sea?
Scientists warn of a possible “gelatinous future” in which jellyfish rule the oceans.
©Nuttawut Uttamaharad/Shutterstock.com
Yet another fascinating aspect of jellyfish biology is their two-part life cycle. They begin life as tiny, bottom-dwelling polyps, which bud off miniature medusae that drift into open water. This transformation is part metamorphosis and part cloning, and gives jellyfish a remarkable ability to rebound after population crashes. Even if every visible jellyfish in a bloom dies off, the polyps can survive unnoticed on rocks, shells, or piers, ready to release a new generation when conditions improve. And some species take this resilience even further.
The so-called “immortal jellyfish” can reverse its life cycle entirely, transforming its adult medusa body back into a polyp stage when stressed. Basically, it can start life over! And humans, not crazy about our own aging process, have taken notice; this feature has become a major focus of aging and regeneration research.
Because of their adaptability, jellyfish are found just about everywhere. They inhabit every ocean, from the Arctic to the tropics, and even some freshwater lakes. They colonize artificial habitats like harbors and offshore rigs. And while they have a reputation for delivering painful or dangerous stings (and some actually do, such as the box jellyfish and Portuguese man-o’-war), most are harmless and constantly brush past swimmers unnoticed.
Some scientists have posited that the ocean could be headed toward a “gelatinous future” dominated by jellyfish and other soft-bodied drifters, due to climate change, overfishing, and pollution, which are reshaping ocean ecosystems in ways that often favor jellyfish. Warmer waters speed up their reproduction, nutrient runoff creates low-oxygen zones where fish struggle but jellyfish thrive, and the removal of large predators allows jellyfish numbers to explode.
But this scenario is only a theory. Many jellyfish blooms are simply part of natural cycles, and ecosystems tend to rebalance as conditions stabilize. Still, given how resilient and adaptable these creatures are—not to mention the fact that they’ve already lasted half a billion years with little to no change to their makeup—it doesn’t seem far-fetched to imagine the oceans populated by nothing but jellyfish from shore to shore!
Happy Jellyfish Day!
For much of history, jellyfish were, at best, curiosities and, at worst, hazards to avoid. But in recent years, scientists, artists, and even chefs are beginning to see them as so much more. Engineers have studied jellyfish propulsion to design soft robots that move gracefully through water. Medical researchers investigate jellyfish collagen for the purposes of wound healing and tissue engineering. Their unique forms and gorgeous transparency have made them icons of climate art and ocean awareness. In several Asian cuisines, jellyfish are considered a delicacy, prepared dried or marinated.
From the luminescent Aequorea of the Pacific to the drifting moon jellies that light up aquariums around the world, jellyfish are literally glowing reminders of the wonder that lies just below the surface. They are living fossils that have watched the planet change again and again, and have survived it all with remarkable beauty and simplicity. This November 3rd, we honor the humble jellyfish, a portrait of resilience itself, with the capacity to persist, adapt, and glow in even the darkest waters.
The post Jellyfish Day Celebrates 500 Million Years of Ocean Wonder appeared first on A-Z Animals.
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